Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Numerator:
Net Income	$ 20,569	$ 12,722	$ 60,076	$ 45,970
Denominator:
Weighted average basic shares (in shares)	31,420	30,520	31,424	29,914
Dilutive potential common shares (in shares)	848	797	856	747
Weighted average fully diluted shares (in shares)	32,268	31,317	32,280	30,661
Earnings per share:
Basic (in dollars per share)	$ 0.65	$ 0.42	$ 1.91	$ 1.54
Diluted (in dollars per share)	$ 0.64	$ 0.41	$ 1.86	$ 1.50
Outstanding common stock equivalents having no dilutive effect (in shares)	0	1	5	10